Red Hat Enterprise Linux allows the first user to log in on the physical console of the
machine the ability to manipulate some devices and perform some tasks
normally reserved for the root user. This is controlled by a PAM module
called pam_console.so.
When a user logs into a Red Hat Enterprise Linux system, the
pam_console.so module is called by
login or the graphical login programs,
gdm and kdm. If
this user is the first user to log in at the physical console —
called the console user — the module
grants the user ownership of a variety of devices normally owned by
root. The console user owns these devices until the last local session
for that user ends. Once the user has logged out, ownership of the
devices reverts back to the root user.
The devices affected include, but are not limited to, sound cards,
diskette drives, and CD-ROM drives.
This allows a local user to manipulate these devices without attaining
root access, thus simplifying common tasks for the console user.
By modifying the file
/etc/security/console.perms, the administrator
can edit the list of devices controlled by
pam_console.so.
 | Warning |
|---|
| | If the gdm,
kdm, or xdm
display manager configuration file has been altered to allow
remote users to log in and the host is
configured to run at runlevel 5, it is advisable to change the
<console> and
<xconsole> directives within the
/etc/security/console.perms to the following
values:
<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :0\.[0-9] :0
<xconsole>=:0\.[0-9] :0 |
Doing this prevents remote users from gaining access to devices
and restricted applications on the machine.
If the gdm,
kdm, or xdm
display manager configuration file has been altered to allow remote
users to log in and the host is configured to
run at any multiple user runlevel other than 5, it is advisable to
remove the <xconsole> directive entirely
and change the <console> directive to the
following value:
<console>=tty[0-9][0-9]* vc/[0-9][0-9]* |
|
The console user is also allowed access to certain programs with a file
bearing the command name in the
/etc/security/console.apps/ directory.
One notable group of applications the console user has access to are
three programs which shut off or reboot the system. These are:
/sbin/halt
/sbin/reboot
/sbin/poweroff
Because these are PAM-aware applications, they call the
pam_console.so module as a requirement for use.
For more information, refer to the Section 16.8.1 Installed Documentation.
